A number of structures are formed of composite materials. For example, many vehicles, such as aircraft, space craft, marine vehicles or the like, include a body that is formed at least partially, if not largely, of composite materials. Regardless of the type of composite structure, a number of composite structures are formed by laying up a plurality of composite plies with each subsequent composite ply being sequentially placed upon a prior composite ply.
During the fabrication of a composite structure, a variety of foreign object debris may be introduced. For example, the foreign object debris may include water, oil or other liquids, fasteners, pieces of wire or other relatively small pieces and parts, or any other type of foreign object. The foreign object debris may come to rest upon a composite ply and, if not removed, may be covered by subsequent composite plies and incorporated into the composite structure. Foreign object debris may create a variety of issues for the resulting composite structure. For example, the foreign object debris may reduce the integrity of the resulting composite structure, may add undesired weight to the composite structure and may adversely impact various material properties, such as the strength to weight ratio, of the composite structure.
As such, the composite structure may be inspected during the fabrication process in an effort to identify and remove foreign object debris. For example, the composite plies may be visually inspected as the composite plies are laid up in order to identify and remove foreign object debris. In order to conduct a thorough visual inspection of a composite ply, however, more time may be required for the visual inspection than would be desired, as at least some of the time required for visual inspection may slow the overall fabrication process. Additionally, it may be difficult to identify, with a visual inspection, foreign object debris that is transparent as well as foreign object debris that does not present a contrast with the background, such as foreign object debris that is black on a black background. Further, performance of the visual inspection process itself may be a source of foreign object debris with the foreign object debris being contributed by the inspector of their clothing or other accessories, such as in instances in which items fall from the inspector's pockets onto the composite structure.
In some cases, it is desirable to increase the rate at which composite structures may be fabricated and/or to allow larger composite structures to be fabricated within a desired time period by increasing the speed with which composite plies are being laid up. However, as the speed with which the composite plies are laid up increases, the time allotted for inspection of the composite plies to identify foreign object debris may be reduced, thereby increasing the difficulties associated with visually inspecting composite plies in a thorough manner to identify foreign object debris during the fabrication of the composite structure. In this regard, the time required for visual inspection may serve as a limiting factor for the speed with which a composite structure is fabricated in some instances.